Steel nut and method of making



Oct. 21, 1952 c. R|EGEL 2,615,119

STEEL NUT AND METHOD OF MAKING Filed Aug. 21, 1947 E1 g E INVENTOR.

I? filg 1/ ATTOHNEY Patented Oct. 21, 1952 STEEL NUT AND METHOD OF MAKING Glen 0. Riegel, Peoria, 111., assignor to Caterpillar Tractor 00., San Leandro, Calif., a corporation of California Application August 21, 1947, Serial No. 769,890

1 Claim.

This invention relates to steel nuts and particularly to the formation of nuts with the area of their hardness pattern best suited to withstand the abuse and stresses to which the different parts of a nut are subjected.

A conventional steel nut is of hexagon shape to present a convenient wrench surface and has two parallel faces between which a threaded bore extends. One of the parallel faces abuts a washer or surface against which the nut is tightened in use and is called the washer face.

-While the main body of the nut should be of comparatively soft steel to permit accurate tapping, the hexagon or wrench surface and the washer face should be hard to prevent deformation by the application of a wrench and by engagement of the nutwith a washer.

One form of nut in common use is made of an alloy steel of medium carbon content capable of being heat-treated. In making such nuts, hexagon bar stock is cut to short lengths, then hard-- ened and then tempered to a softness adapted to practical machine operations of boring, reaming and tapping. This leaves the wrench surface and washer face too soft to withstand satisfactorily the stresses and abuse to which they are subjected in hard use.

' Nuts are also made of low carbon steel incapable of being directly hardened but subject to being carburized so that subsequently they can be surface-hardened. In making these nuts the blanks are cut to length from bar stock, then carburized and bored. As the bore is not carburized, subsequent heat treatment will surface harden a nut except in its bore and it may then be tapped, reamed and counter-bored. While the nuts so made are superficially harder than those made of alloy steel with the softer surfaces, they are still subject to deformation by a wrench and in many cases the relatively shallow hardened washer surface cracks, usually radially from the bore, and presents sharp edges to dig in or cut the washer against which it is drawn.

It is an object of the present invention to provide a method of making a nut with a hardened wrench surface and with a deeply penetrating and harder washer face while at the same time permitting a softer, machinable bore for accurate final tapping.

The invention has other objects and advantages that will become apparent from an understanding of the following specifications wherein reference is made to the accompanying drawings.

In the drawings:

Fig. l is a transverse sectional View through a nut made in accordance with the present invention;

Fig. 2 is a longitudinal section view through the same nut;

Fig. 3 is a plan view of a heat-inducing element with the induction circuit diagrammatically shown and illustrating the position assumed by a nut being treated;

Fig. 4 is a fragmentary View in elevation of a series of nuts supported on a mandrel ready for treatment in an induction device illustrated in section; and

Fig. 5 is a section taken on the line VV of Fig. 3 showing nuts supported on a mandrel and just entering the heat-inducing field.

The invention takes advantage of a phenomenon of induction hardening that is particularly apparent where a piece of bar stock or the like is passed longitudinally through an inducing field. The heating of the stock is substantially even throughout its entire length. However, as the stock enters the field, its very end disposed at right angles to its longitudinal side walls effects a disturbance of the field to produce a distortion or eddying condition. The result is that the leading end of the stock is heated to a greater temperature and the heat penetrates more deeply than elsewhere. Therefore, upon subsequent quenching, the side walls of the stock are found to be hardened to a uniform depth throughout its length except at its leading end where the depth of the hardening is very much greater.

According to the present invention this phenomenon is employed to produce a superior steel nut. The nut blanks are first formed of steel of suitable carbon content for heat treatment, then hardened and tempered to machinable hardness and then passed in the direction of their axes through a heat-inducing field. The washer faces of the nuts or nut blanks are all arranged to enter the field first and therefore become more deeply hardened than the wrench surfaces. For example, and by reference first to Figs. 1 and 2 of the drawings, a nut II] of typical shape is shown as having hexagonal wrench surfaces II, a washer face I2 and a threaded bore I3. It is conventional practice to counterbore the nut, as illustrated at I4, adjacent its washer face and also to relieve or cut back the outer edge of the washer face, as indicated at I5, in order to provide an annular engaging face for contact with the washer. At its opposite end the nut may be left as shown or may be counter-sunk slightly at its bore and chamfered at its outer periphery.

By arranging nuts in axial alignment and passing them with their washer faces in a leading position through a heat-inducing field, the wrench. surfaces may be hardened to a depth indicated by the shading it while the washer faces will be provided with a greater hardness of greater depth, as indicated by the darker shading I! in Fig. 2. In the manufacture of a nut to be induction hardened in this manner, hexagon bar stock is first cut to suitable lengths and then bored. The nut blank so formed may then be counter-bored, counter-sunk and trimmed and chamfered as required. The blank is then hardened throughout by any conventional process such as heating and oil quenching and is tempered to a machinable hardness, such for example as a Rockwell hardness of from B95 to B102, so that the bore may be reamed and tapped after the wrench surface and washer face have been subjected to induction hardening.

In order to provide induction hardening of the character and distribution indicated by the shaded areas in Fig. 2 of the drawings, the nuts are either taken singly or aligned in end-toend relation and passed through a substantially circular electrical induction unit, such as indicated at 29 in Fig. 3. This unit has separated legs 24 connected in a circuit 22, which includes a generator 23 and usually also a variable condenser 24 for regulating the intensity of the heat-inducing field. In order to pass the nuts through the field in a rapid and efficient manner, a series of nuts, as is indicated at 25 in Fig. 4, may be arranged on a mandrel 25 provided with a supporting collar 27. The mandrel 26, preferably formed of non-ferrous material, is then rotated continuously by any suitable mechanical means (not shown) and passed in a downward direction, as illustrated in Fig. 4, centrally through the induction element 29. The lines of fiux of the induction field as it is interrupted by passing the nuts therethrough are indicated diagrammatically by broken lines 28 in Figs. 3 and 5. Thus as the nuts progress through the field, their outer or wrench surfaces are evenly heated to a relatively shallow depth, as indicated at IS in Fig. 2, and in a manner comparable to the heating of a length of bar stock. However, as the leading or washer face of each nut enters the field it interrupts and disturbs the uniform characteristics of the flux with the result that eddying and distortion takes place to produce a greater and more penetrating heat adjacent the washer face, as characterized by the shaded area I! in Fig. 2. Consequently, upon quenching, which is effected usually by a conventional water spray (not shown) disposed adjacent and preferably below the induction element 20, the hardness is distributed in a manner illustrated in Fig. 2 to produce a nut with a relatively soft body or core member of high yield strength with a hard wrench surface and with an even harder and more deeply penetrating washer face. The extent of the hardness at the washer face is sufilcient to prevent the development of the usual radial cracks which interfere with the proper tightening of the nut against a washer, and the hardness on the wrench surface is adequate to withstand the application of pressure by a wrench in tightening the nut.

In practice nuts manufactured in this manner have been rapidly and efiiciently manufactured with washer faces of Martensitic hardness and with a wrench surface just slightly less hard without unduly hardening or reducing the yield strength of the main body or core of the nut.

The nuts herein disclosed are shown to be of a particular shape and are shown as counter-bored and trimmed in a conventional manner. It is apparent, however, that nuts varying from the specific shape herein illustrated may readily be made by the process described and will include the advantages of this invention. The degree and extent of hardness of nuts treated by the method of this invention may, of course, be varied by regulation of the strength of the heatinducing field, by regulation of the speed at which the nuts move as they pass through the field, or by subsequent tempering as desired.

I claim:

The method of preparing and heating blanks for steel nuts in a hardening process to provide a hard wrench surface and a hardened washer face which comprises, cutting away a portion of the exterior of the nut adjacent the washer face, then passing a plurality of nuts through a high frequency current heat inducing field with the nuts in contact with each other and their washer faces in a leading position.

GLEN C. RIEGEL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number OTHER REFERENCES Qsborn: The Tocco Process, published by The Ohio Crankshaft 00., Cleveland, Ohio, 1943, pages 18 and 19. 

